This invention relates generally to methods for beneficiation of minerals, and more specifically relates to a method for improving the brightness of minerals such as kaolin clays, through the use of magnetic separation.
Naturally occurring minerals such as natural clays, carbonates, talcs or so forth, frequently include discoloring contaminants in the form of iron and/or iron-stained titanium-based impurities. The present invention has particular applicability to natural clays, including kaolin clays, and it may be noted in this connection that the quantities of the aforementioned titanium-based discolorants are particularly significant in the case of the sedimentary kaolins of Georgia, where such impurities are commonly present as iron-stained anatase and rutile.
In the case of the kaolin clays and others of the minerals mentioned, it is often desired and sometimes imperative to refine the natural product and bring the brightness characteristics thereof to a level acceptable for paper coating and other applications. Various techniques have been used in the past to effect the removal of the aforementioned discoloring impurities. Thus, for example, hydrosulfites have been widely used for converting at least part of the iron-based (or "ferruginous") impurities to soluble form, which may then be removed from the clays.
Among the most effective methods for removing titaniferous impurities, including e.g. iron-stained anatase, are the well-known froth flotation techniques. According to such methods an aqueous suspension or slurry of the clay is formed, the pH of the slurry is raised to an alkaline value, for example, by the addition of ammonium hydroxide, and a collecting agent is added, as for example, oleic acid. The slurry is then conditioned by agitating same for a relatively sustained period. A frothing agent, such as pine oil is then added to the conditioned slurry, after which air is passed through the slurry in a froth flotation cell to effect separation of the impurities.
Within recent years it has, further been demonstrated, that high intensity magnetic separation techniques may be utilized for removing certain of the aforementioned impurities, including titaniferrous impurities, and certain ferruginous matter. Anatase, for example, and certain other paramagnetic minerals, have been found to respond to high intensity magnetic fields. Thus in U.S. Pat. No. 3,676,337 to Henry H. Kolm for example, a process is disclosed for treating mineral slurries or the like, by passing same through a steel wool matrix in the presence of a background filed of at least 12,000 Gauss. Various apparatus, such as that disclosed in Marston, U.S. Pat. No. 3,627,678, may be utilized in carrying out the cited processes. In this latter instance the slurry to be treated is thus passed through a canister, which contains a stainless steel or similar filamentry ferromagnetic matrix, while a high intensity magnetic field is impressed on the matrix by enveloping coils.
While the use of high intensity magnetic separation as outlined in the foregoing paragraph, has found a high degree of acceptance in certain mineral beneficiation technology -- most notably in the brightening of kaolins -- it has generally been believed up until the present time, that such technology was not in fact capable of producing brightness improvements attainable by the use of the aforementioned flotation techniques. Neither, of course, has it been contemplated that field intensity levels of the low to intermediate type could be of value in brightening kaolins or the like, to commercially acceptable levels.
In accordance with the foregoing, it may be regarded as an object of the present invention, to provide a method for magnetic separation of discoloring contaminants from mineral slurries, such as kaolin slurries, which method enables brightness improvements previously unattainable through magnetic separation processes.
It is a further object of the present invention, to provide a method for magnetically beneficiating mineral slurries such as kaolins, which method yields brightness improvements at sufficiently high levels to obviate any requirement for flotation treatments.
It is a yet further object of the present invention, to provide a method for magnetic separation of discoloring contaminants from mineral slurries, which is based upon the use of particulate magnetic activating agents, of a type which are producible at low costs, and which have little or no detrimental impact upon the environment.
It is a still further object of the invention, to provide a method for magnetic separation of discoloring contaminants from kaolin slurries or the like, which enables the use of lower field intensities than have heretofore been deemed appropriate or feasible for such purposes.
It is a yet further object of the invention, to provide a method for magnetic separation of discoloring contaminants from kaolin slurries or the like, which may be utilized with existing magnetic separation apparatus, and which vastly increases the performance capabilities of such devices.